The present invention relates to a method and a device of the type mentioned in the preambles of the independent claims for controlling the movement of moving parts in a milking machine.
Automatic milking machines are known in which a robot arm is used to move various attachments such as teat cups and cleaning devices from docking stations on for example the frame of the machine to working positions, for example under the udder of the animal being milked. The movement of the robot arm is controlled by a computer, which determines a desired position for the attachment and operates actuators on the arm in a controlled manner in order to bring the attachment to the desired position. The computer determines the distance in the x-, y-, z- and rotational axes between the current position and the desired position and commands each of the x-, y-, z-axes and rotational actuators to respectively extend, retract or rotate the necessary amount in order to move the robot arm to the desired position. The computer is provided with a programme, which determines the speed of extension retraction of the actuators and the computer can thereby predetermine how much time the movement from the actual position to the desired position should take. At the end of the predetermined time the computer compares the actual position of the attachment against its desired position. If the actual position is not the same as the desired position the computer determines that an error has occurred and can take further corrective action or produce an alarm signal.
EP 0 300 115 A1 discloses a device for automatic milking of cows, in which a memory contains data on usual teat positions used for locating teats on a cow to be milked. This data on teat positions is continuously corrected in response to changes in conditions.
A problem occurs if the robot arm is in contact with an obstacle, such as an operator or a part of an animal, which is in the path of the robot arm. It is possible that injuries can be caused or aggravated during the time between the contact occurring and the end of the predetermined time.
An object of the present invention is to provide a method and device which does not suffer from the problems of the prior art devices.
According to the invention, the above problem is solved by a method and device having the features stated in the characterising parts of the independent claims. The invention thus relates to a method and a device comprising modelling means for calculation of a predicted path that a robot arm will follow when moving from an actual position to a desired position and comparing means for comparing the actual path of the robot arm against the modelled predicted path.